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Award Ceremony Speech

Presentation Speech by Professor C.G.
Bernhard, Member of the Nobel Committee for Physiology or
Medicine of the Royal
Caroline Institute

Your Majesty, Royal Highnesses, Ladies and
Gentlemen.

Light, shadows and colours do not exist in the world around us.
What we perceive visually and call light is the result of the
action of a certain portion of the electromagnetic radiation on
the sensory cells in the retina of the eye. Our awareness of the
play of light in nature, the multiplicity of the forms and the
richness of the colours is ultimately dependent on the pattern of
this radiation with respect to frequency and intensity. The light
is composed of packets of energy, which combine the properties of
waves and particles. When these particles - the quanta - strike
the retina of the eye they are caught by the specialized sense
cells - rods and cones. It is known that one quantum, which
represents the least possible amount of light, is sufficient to
initiate a reaction in a single rod. The excitation of the
sensory cells results in messages directed towards the brain. As
there are no direct connections from the eye to the brain the
messages must be transmitted through several relays which combine
signals from several sensory cells and translate the message into
a language which can be understood by the brain. The primary
relay is in the retina itself, represented by an intricate nerve
net, the structural beauty of which was revealed by the
neurohistologist Ramón y
Cajal, Nobel laureate of 1906. In this complex structure
messages from a great number of sensory cells converge on a far
smaller number of optic nerve fibers and this results in a
transformation of the pattern of signals.

Picasso has said: «To me painting is a sum of destructions.
I paint a motif, then I destroy it». The painting goes
through a series of metamorphoses but «in the solution of
the problem nothing has been lost. The final impression is still
there in spite of all revisions». However, it is obvious to
everyone that in the finished work a re-evaluation has taken
place of the original elements of the motif. In some way this is
a description of what happens in the visual system. An image of
the outer world is formed on the retina in the same way as it is
formed in the film of the camera. The image that falls on the
closely packed mosaic of light sensory cells is disintegrated,
since different cell types respond to various parts and qualities
of the image. The primary data are then brought together in the
nerve net in which a considerable processing takes place
involving not only addition but also subtraction. This
characterization of the message induces an impression in which
there is a re-evaluation of the image projected on the retina.
Does it mean that we cannot rely on what the eye tells us? No,
not in the sense that there is full agreement between the
external stimulus pattern and the composition of the impression.
But rather in the sense that certain characteristics of the
picture with essential biological and psychological significance
are emphasized. There is a sharpening of contrast so that forms
stand out more clearly, colours are exaggerated and movements
accentuated.

We now know the mechanism by which light triggers off the
reaction in the sensory cells of the eye thanks to the
discoveries by George Wald and his coworkers among whom Ruth
Hubbard - now Mrs. Wald - should be mentioned in the first place.
The light-sensitive substances in the sensory cells, the visual
pigments, consist in principle of two pieces. One, containing
vitamin A, the smaller piece or the chromophore, fits like a
hooked puzzle piece in the surface profile of the larger protein
piece, the opsin. When a light quantum is taken up by the visual
pigment the chromophore changes its form: there is an
isomerization from II-cis to all-trans. The puzzle
piece straightens out and releases itself from its position so
that a successive splitting of the visual pigment follows. This
molecular transformation induced by light - the isomerization
triggers the subsequent events in the visual system. All later
changes - chemical, physiological and psychological - are as Wald
says «dark» consequences of this single light reaction.
Wald's conclusion that this reaction applies to the whole animal
world also emphasizes the broad significance of his
discovery.

Our ability to differentiate colours requires that different
visual cells respond characteristically to different parts of the
spectrum. Theories concerning the physiological basis of colour
vision originated with Isaac Newton, Thomas Young and Hermann von Helmholtz. These theories were
based on perception experiments. Today it is possible to attack
this problem more directly with the aid of electronics which
permits interpretation of the language of the nerve cells, thanks
to the pioneer work in the 1920's by E.D. Adrian, Nobel laureate 1932. It is
a great pleasure to see Lord Adrian here today and in this
context I am reminded of his work with Yngve Zotterman which 40
years ago taught us the ABC's of the symbols in the sensory
cells' language.

We honour Ragnar Granit for his discovery of elements in the
retina possessing differential spectral sensitivities as
determined by means of electrophysiological methods. The first
work together with Svaetichin appeared in 1939. It was followed
by an impressive series of investigations which led to the
conclusion that there are different types of cones representing
three characteristic spectral sensitivities. This important
conclusion of Granit has recently been confirmed by Wald and
collaborators as well as by research groups in U.S.A. and Great
Britain using other methods. The discovery implies that the
signal patterns which the optic nerve transmits to the brain and
which result in perception of colours are dependent on the
contributions from the three types of cone cells.

Keffer Hartline's elegant analysis of impulse generation in the
sensory cells and the code they transmit in response to
illumination of different intensity and duration has given us the
basic understanding of how they evaluate the light stimulus. His
later studies have led to the discovery of fundamental principles
according to which the rough data from the sensory cells are
re-evaluated. A precise quantitative analysis of the results was
made possible by a refined technique and a careful choice of a
suitable object - the eye of the horseshoe crab, a large marine
spider. This approach to the problem led him to the discovery of
the lateral inhibition, which in this eye was shown to be
mediated by simple neuronal connections. Already in the 1930's
Granit had shown the existence and importance of inhibition in
the complex vertebrate retina. After having shown the
interconnections of adjacent visual cells Hartline employed his
discovery in a most imaginative way in order to obtain a
quantitative description how a nerve-net processes the data from
the sensory cells by means of inhibition. His discoveries have in
a unique manner contributed to our understanding of the
physiological mechanism whereby heightened contrast sharpens the
visual impressions of form and movement.

Professor Granit, Professor Hartline,
Professor Wald. Your discoveries have deepened our insight into
the nature of the subtle processes in the eye which form the
basis of our ability to perceive light and to distinguish
brightness, colour, form and movement. They have also proved to
be of paramount importance for the understanding of sensory
processes in general.

Professor Granit. About 100 years ago the
distinguished physiologist in Uppsala, Frithiof Holmgren,
discovered the electrical response of the eye to light. The hopes
that he expressed for the future regarding the possibilities of
all electrophysiological analysis of the retinal processes and
the mechanism of colour vision have been realized by your
distinguished discoveries. These show the importance of
inhibition in the integrative action of the retina and the
principles for spectral discrimination by retinal elements. Your
discoveries have pointed the way in modern physiology of vision
and your stimulating research work has contributed to the
fruitful development of this field.

Professor Hartline. Your laboratory has
been described as a «slightly disorganized but extremely
fertile chaos». Your work which - by the same right has been
characterized by «elegance in design, expertise in
manipulation and clarity in exposition» has resulted in an
exemplary limited number of publications, each of which is a
corner-stone in sensory physiology. They have given us the basic
knowledge about the impulse coding in the visual receptors and
presented discoveries of the most fundamental principles for data
processing in neuronal networks which serve sensory functions. In
the case of vision they are vital for the understanding of the
mechanisms underlying perceptions of brightness, form and
movement.

Professor Wald. With a deep biological
insight and a great biochemical skill you have successfully
identified visual pigments and their precursors. As a byproduct
you were able to describe the absorption spectra of the different
types of cones serving colour vision. Your most important
discovery of the primary molecular reaction to light in the eye
represents a dramatic advance in vision since it plays the role
of a trigger in the photoreceptors of all living animals.

Gentlemen. It is with great satisfaction
that Karolinska Institutet has decided to award you this year's
Nobel Prize for physiology or medicine for your discoveries
concerning the primary physiological and chemical visual
processes. On behalf of the Institute I wish to extend to you our
warm congratulations and I ask you to receive the prize from the
hands of His Majesty the King.